Silica-grafted xanthan gum settling agent, its preparation method and application

Abstract

This invention discloses a silica-grafted xanthan gum settling agent, whose raw materials are mainly composed of silica, ammonium persulfate, and xanthan gum. Xanthan gum is a readily available natural raw material. An inorganic-organic composite settling agent is prepared by graft copolymerization of silica and xanthan gum, exhibiting good settling effect and a significant decrease in the apparent viscosity of raffinate after settling. It can be used as a settling agent for raffinate, and its good settling effect is achieved when used alone or in combination with polyacrylamide.

Description

Technical Field

[0001] This invention belongs to the technical field of residual acid settling agents, specifically relating to silica-grafted xanthan gum settling agents, their preparation methods, and applications. Background Technology

[0002] Raffinate is the acid remaining after the extraction of wet-process phosphoric acid. After extraction and purification, most impurities, including various ionic (anionic and cationic) impurities and insoluble impurities, are enriched in the raffinate. After a large amount of phosphoric acid is extracted to the organic phase by organic solvents, anionic and cationic impurities that are insoluble or slightly soluble in organic solvents, as well as solids, are enriched in the raffinate, resulting in a much higher impurity content than wet-process phosphoric acid. Due to the presence of these impurity ions, raffinate has high viscosity and is prone to scaling, making it difficult to use directly in production.

[0003] Xanthan gum is a microbial extracellular polysaccharide produced by the fermentation of *Xanthomonas auricula-judae*. It appears as a light yellow to white free-flowing powder and is a high-molecular-weight polymer composed of D-glucose, D-mannose, and D-glucuronic acid in specific proportions. Xanthan gum's unique double-helix structure is the basis for its stable performance. The number of pyruvate groups at the ends of its molecular side chains directly affects its properties, exhibiting high viscosity at low concentrations, achieving ideal thickening effects with minimal dosage. Traditional flocculants fail to achieve rapid sedimentation of residual raffinate and hinder its subsequent processing. Furthermore, no flocculant for residual raffinate has been developed based on xanthan gum. Therefore, a flocculant suitable for the sedimentation of residual raffinate needs to be developed. Summary of the Invention

[0004] The purpose of this invention is to address the technical problems of high impurity ion content, high viscosity, easy scaling, and difficulty in direct utilization of residual acid. This study proposes to use silica, a by-product of anhydrous hydrogen fluoride plant, as a carrier and xanthan gum as a skeleton to successfully prepare a SiO2-grafted inorganic-organic composite flocculant with characteristics such as fast sedimentation rate and good sedimentation effect.

[0005] According to a first aspect of the present invention, a silica-grafted xanthan gum settling agent is provided, which is mainly prepared from silica, ammonium persulfate and xanthan gum, wherein the mass ratio of silica, ammonium persulfate and xanthan gum is 1:(0.05-0.09):(0.7-0.9).

[0006] The silica-grafted xanthan gum precipitant of the present invention uses xanthan gum as a skeleton and is obtained by grafting silica. As a precipitant, it can exhibit high degradation efficiency under residual acid at 70-90℃, and has the characteristics of fast sedimentation rate and good sedimentation effect.

[0007] In some embodiments, the particle size of silica is 25-35 μm. Preferably, the particle size of silica is 30 μm. It should be noted that when the particle size of silica is too large, SiO2 is difficult to disperse in low molecular weight aqueous solution, and aggregation occurs, which reduces the effective specific surface area, hinders the diffusion of xanthan gum molecules, reduces the grafting rate, and affects the sedimentation effect of silica-grafted xanthan gum flocculant.

[0008] In some embodiments, silicon dioxide is prepared by mixing silicon dioxide with a 1 mol / L hydrochloric acid solution or nitric acid solution, stirring for 20-40 min, washing and drying to obtain the final product.

[0009] In some embodiments, the specific surface area of ​​silica is 1100-1300 m². 2 / kg.

[0010] In some embodiments, silica can also be a byproduct of an anhydrous hydrogen fluoride unit, i.e., silica produced as a byproduct of anhydrous hydrogen fluoride production via fluorosilicic acid recovery (see "TGZHG 037-2025 Silica Produced as a Byproduct of Anhydrous Hydrogen Fluoride Production via Fluorosilicic Acid Recovery"). It can be a byproduct obtained through pressure filtration and dehydration after hydrolysis of fluorosilicic acid. Fluorosilicic acid hydrolysis is an important step in the production and recovery process of wet-process phosphoric acid. Methods for obtaining silica through fluorosilicic acid hydrolysis are commercially common, such as reacting fluorosilicic acid solution with ammonia followed by pressure filtration and dehydration.

[0011] In some embodiments, the mass-to-volume ratio of silicon dioxide to hydrochloric acid solution or nitric acid solution is 1:0.8 to 1:1.

[0012] In some embodiments, the mass ratio of silica, ammonium persulfate, and xanthan gum is 1:(0.05-0.09):(0.7-0.9). Preferably, the mass ratio of silica, ammonium persulfate, and xanthan gum is 1:0.07:0.83.

[0013] According to a second aspect of the present invention, a method for preparing the above-mentioned silica-grafted xanthan gum settling agent is provided, comprising the following steps: (1) Disperse xanthan gum in deionized water, heat to 45-55℃, add ammonium persulfate to the deionized water, and react for 0.5-2.5 h to obtain a low molecular weight aqueous solution; (2) Add silica to a low molecular weight aqueous solution at 700-900 rpm, and then add a 10% ammonium persulfate solution to the low molecular weight aqueous solution under an inert gas atmosphere and at 45-55℃. Stir the reaction at 400-600 rpm for 5.5-7 h to obtain the product.

[0014] In some embodiments, the amount of ammonium persulfate in the low molecular weight aqueous solution is 5-9 mmol / L.

[0015] In some embodiments, in step (1), each 1 gram of xanthan gum is dispersed in 40-60 mL of deionized water.

[0016] In some implementations, the inert gas in step (2) is nitrogen.

[0017] In some embodiments, in step (2), the amount of silica in the low molecular weight aqueous solution is 0.1~0.5 mol / L. Preferably, the amount of silica in the low molecular weight aqueous solution is 0.4 mol / L.

[0018] The preparation method of the present invention first decomposes xanthan gum with ammonium persulfate (APS) to shorten the molecular chain and improve the chain segment mobility, thereby obtaining small molecular chains with low steric hindrance. Then, the small molecular chains can diffuse to the SiO2 surface and undergo effective collisions, resulting in a flocculant with high graft density and good sedimentation effect.

[0019] According to a third aspect of the present invention, the above-mentioned silica-grafted xanthan gum precipitant is provided for use in the preparation of raffinate precipitant.

[0020] Specifically, silica-grafted xanthan gum settling agent can be used alone as a settling agent for residual acid precipitation, or it can be used in conjunction with acrylamide to achieve residual acid precipitation.

[0021] When silica-grafted xanthan gum flocculant is thoroughly mixed with residual raffinate, its large molecular weight and long molecular chains allow it to act as a "bridge," interacting with particles through its active groups to connect them and form flocs. This bridging effect allows more impurity particles and small flocs to connect better, gradually agglomerating into larger flocs with more molecular chains. These larger flocs then more easily adsorb and trap more and more impurity particles during gravity settling, resulting in large and dense flocs.

[0022] In some embodiments, for every 100 mL of residual raffinate, the amount of silica-grafted xanthan gum precipitant used is 0.4-0.8 mL, and the amount of acrylamide used is 0.5-1 mL.

[0023] In some embodiments, when silica-grafted xanthan gum precipitant is used as a precipitant for residual raffinate, the method of use is to preheat the residual raffinate at 70-90°C for ten minutes, and then add the silica-grafted xanthan gum precipitant and disperse it for 20-80 seconds.

[0024] The beneficial effects of this invention are as follows: (1) The silica-grafted xanthan gum precipitant of the present invention is prepared by graft copolymerization based on the properties of raffinate, using silica particles as carrier and natural raw material xanthan gum as organic skeleton. The precipitant developed based on xanthan gum has good precipitating effect and the apparent viscosity of raffinate decreases significantly after precipitation. (2) The sediment obtained by treating residual acid with silica-grafted xanthan gum precipitant of the present invention contains a lot of metal elements, which can remove metal ions from residual acid and is beneficial to the subsequent phosphorus recovery of residual acid. (3) The silica-grafted xanthan gum settling agent of the present invention has good settling efficiency at 70-90℃ and can be used as a settling agent for residual acid. When used in combination with polyacrylamide, it has a good settling effect on residual acid. Attached Figure Description

[0025] Figure 1 The image shows the FTIR spectrum of SiO2-XG from this invention. Figure 2 These are FTIR images of low molecular weight aqueous solutions at different reaction times according to the present invention; Figure 3 The sedimentation effect of silica-grafted xanthan gum flocculant with different amounts of ammonium persulfate was investigated. Figure 4 Sedimentation effects of silica-grafted xanthan gum flocculants with different SiO2 addition amounts; Figure 5 The SiO2-XG dosage curve of this invention; Figure 6 The sedimentation effect of SiO2-XG at different dispersion times; Figure 7 The sedimentation effect of SiO2-XG at different temperatures; Figure 8 The shear rate variation curve of SiO2-XG in this invention is shown. Figure 9 Infrared spectra of precipitates obtained from raffinate treated with different settling agents; Figure 10 XRD analysis of the sediment obtained from SiO2-XG treatment of residual acid in this invention; Figure 11 The XPS full spectrum of the sediment obtained by treating residual acid with SiO2-XG according to this invention; Figure 12 and Figure 13 XPS analysis of the sediment obtained from SiO2-XG treatment of residual acid in this invention; Figure 14 EDS analysis of the sediment obtained from the SiO2-XG treatment of residual acid in this invention. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0027] I. Raw Materials and Reagents The SiO2 byproduct and residual acid from the anhydrous hydrogen fluoride unit used in the experiment were both provided by Guizhou Phosphate Group. The main composition and properties of the residual acid are shown in Table 1. The main component of the residual acid is P2O5, with a content of 47.19%. The contents of water-insoluble matter and organic carbon are 6.70% and 0.019%, respectively.

[0028] Table 1 Basic parameters of residual acid

[0029] The main reagents used in the experiment (all analytical grade) were: polyacrylamide (from Guizhou Phosphate Group); xanthan gum (from Shandong Keyuan Biochemical Co., Ltd.); and ammonium persulfate (from Tianjin Fuchen Chemical Reagent Co., Ltd.). Deionized water was used in all experiments.

[0030] It should be noted that the silica powder used in the embodiments and experiments of this invention can be SiO2 by-product of an anhydrous hydrogen fluoride plant, for example, derived from a concentrated sulfuric acid decomposition process using fluorosilicic acid, a by-product of wet-process phosphoric acid, as raw material. In this process, fluorosilicic acid (H2SiF6) reacts with concentrated sulfuric acid in a reactor to generate anhydrous hydrogen fluoride (HF) and silicon fluoride (SiF4). SiF4 is then absorbed by water / dilute fluorosilicic acid in an absorption tower and hydrolyzed to generate SiO2 precipitate (3SiF4 + 2H2O → 2H2SiF6 + SiO2↓). By-product silica is obtained through solid-liquid separation. A small number of plants use a thermal decomposition-hydrolysis route, which also generates SiO2 in the subsequent hydrolysis stage. The by-product SiO2 produced in this process is also the by-product SiO2 of the anhydrous hydrogen fluoride plant of this invention, and both are existing products obtained using existing technology.

[0031] The resulting SiO2 contains impurity ions including Fe, Mg, Al, and some dust, and is in a disordered state. The silica used in the example has a particle size of approximately 30 μm and a specific surface area of ​​1126 m². 2 / kg, the volume average diameter D[4,3] is 34.9 μm, the area average diameter D[3,2] is 5.33 μm, and the median volume diameter D V (50) is 6.35 μm.

[0032] Acid-washed silica is prepared by the following method: A 1 mol / L hydrochloric acid or nitric acid solution is prepared, silica powder is added and stirred for 30 min, washed with deionized water, and then dried in an oven. The mass-to-volume ratio of silica to the hydrochloric acid or nitric acid solution is 1:0.8-1:1, meaning that every 1 g of silica is acid-washed with 0.8-1 mL of a 1 mol / L hydrochloric acid or nitric acid solution. The purpose of acid washing is primarily to remove existing impurity ions and dust from the silica powder.

[0033] Example 1 This embodiment provides a method for preparing a silica-grafted xanthan gum settling agent, comprising the following steps: (1) Take 2g of xanthan gum and disperse it in 100mL of deionized water. Heat it to about 50℃, add 0.16g of ammonium persulfate to the deionized water, and react for 2h to obtain a low molecular weight aqueous solution.

[0034] (2) Take 2.4 g of acid-washed silica powder, add a low molecular weight aqueous solution at 800 rpm, purge with nitrogen for 10 min to remove oxygen, heat to 50℃, add 5 mL of 10% ammonium persulfate solution, and stir the reaction for 6 h under nitrogen and 500 rpm conditions. Dry under vacuum at 60℃ to obtain the product. The silica-grafted xanthan gum precipitant prepared in Example 1 is denoted as SiO2-xanthan gum (SiO2-XG).

[0035] The silica-grafted xanthan gum settling agent prepared in Example 1 was subjected to infrared spectroscopy analysis. At room temperature, the settling agent and the resulting residue were analyzed using a Nicolet 380 Fourier transform infrared spectrometer (Thermo Scientific, Japan) at 400-4000 cm⁻¹. -1 wavenumber range and 4cm -1 FTIR testing was performed at a high resolution. The settling agent and residue were ground into powder, mixed with KBr powder, and then compressed into particles for testing.

[0036] FTIR spectrum as shown Figure 1 As shown. In Figure 1 Middle, 1628cm -1 The peak at that point represents COO in pyruvate. - Stretching vibration absorption peak, SiO 2- The enhanced peak at XG is due to the oxidative degradation and breakage of the xanthan gum backbone under ammonium persulfate oxidation. This degradation results in the long chains becoming shorter oligosaccharide chains, which are then grafted onto SiO2. This significantly increases the proportion of glucuronic acid units at the chain ends in the grafted product. Therefore, in the same mass of sample, the signal of the carboxyl group is stronger relative to the signal of the backbone. (1100 cm⁻¹)-1 The peak at 930 cm⁻¹ represents the covalent bond Si-OC formed by the condensation reaction of the silanol groups of SiO₂ with the hydroxyl or carboxyl groups of xanthan gum; -1 The peak at 800 cm⁻¹ is Si-OH, and the decrease in this peak at XG-SiO₂ indicates that the surface silanol groups participated in the grafting reaction; -1 The peaks at the left and right positions represent Si-O-Si symmetric stretching vibrations. These spectral changes collectively confirm that xanthan gum was successfully grafted onto the silica surface.

[0037] II. Examination of Preparation Methods The preparation method of Example 1 was adjusted, and its effect was investigated through sedimentation experiments.

[0038] 1. Testing Method Sedimentation experiments were conducted in a graduated cylinder, and the sedimentation effect was determined by the volume of the supernatant and the volume of the precipitate during the sedimentation process. The residual raffinate used in the experiment was preheated at 70℃ for ten minutes, removed, stirred evenly, and 100 mL of the residual raffinate was accurately measured and poured into the graduated cylinder. Then, 0.5 mL of polyacrylamide flocculant (PAM) was added and dispersed for 60 seconds to ensure uniformity. Next, 0.4 mL of the prepared SiO2-XG was added, and the mixture was dispersed again for 40 seconds to ensure uniformity. The cylinder was then placed in a 70℃ water bath for natural sedimentation at a constant temperature, and the height of the clarified layer was recorded at regular intervals. Following the above steps, the optimal preparation method of the sedimentation agent was determined by changing the reaction conditions and the amount of raw materials used.

[0039] 2. Effect of oxidation time on sedimentation effect Different reaction times (0.5-3 h) were selected in step (1), and the FTIR of the low molecular weight aqueous solution (XG) was detected. The results are as follows: Figure 2 As shown.

[0040] FTIR spectra of low molecular weight aqueous solutions at different reaction times are as follows: Figure 2 As shown in (a). By Figure 2 (a) It can be seen that the characteristic absorption peak of xanthan gum, namely 3463 cm⁻¹, was retained at different oxidation times. -1 The stretching vibration peaks at -OH are at 1628 and 1592 cm⁻¹. -1 The COO- stretching vibration absorption peaks in pyruvate esters are at 1382 and 1358 cm⁻¹. -1 The in-plane bending vibration absorption at the -CH peak indicates that the basic structural units of xanthan gum remain intact after degradation. With increasing oxidation time, the -OH peak shifts to lower wavenumbers, from 3463 cm⁻¹. -1 up to 3430cm -1 This indicates that the degraded xanthan gum oligosaccharides formed more intramolecular or intermolecular hydrogen bonds, possibly due to the exposure of more hydroxyl groups during degradation. And 1628cm -1The peak at 1623 cm⁻¹ intensifies with prolonged oxidation time. This is because during degradation, the breakage of polysaccharide chains may expose more pyruvate groups, resulting in a relative increase in carbonyl density per unit mass, thus leading to the higher peak at 1623 cm⁻¹. -1 The peak intensity increased slightly, but the change in peak intensity was no longer significant after 2 hours. Figure 2 (b) The effect of oxidation time on sedimentation shows that 2 hours yields the best degradation effect. This is likely because the oxidation and decomposition time of xanthan gum directly determines the chemical structure of the precursor (xanthan gum degradation products), thus affecting the subsequent grafting reaction with silica and consequently the sedimentation effect. When the oxidation time is insufficient, APS decomposition is incomplete, the free radical concentration is low, which may lead to incomplete xanthan gum degradation, resulting in long molecular chains, poor chain segment mobility, large steric hindrance, and a low proportion of active sites that can diffuse to the SiO2 surface and undergo effective collisions, leading to low grafting density and mostly physical entanglement of grafted molecules, resulting in poor sedimentation. As the oxidation time increases, free radical generation is accelerated, making the xanthan gum molecular chains break more completely and significantly reducing the molecular weight. When the oxidation time is too long, xanthan gum is over-degraded, generating too many small molecular fragments. Active groups may be destroyed or transformed into other forms, leading to a decrease in grafting density and thus affecting the sedimentation effect.

[0041] 3. Effect of ammonium persulfate dosage on sedimentation effect In step (1), the amount of ammonium persulfate added was selected to be 5-9 mmol / L, and the other steps were the same as in Example 1, to prepare silica-grafted xanthan gum precipitants with different amounts of ammonium persulfate. The sedimentation effects of silica-grafted xanthan gum precipitants with different amounts of ammonium persulfate are as follows: Figure 3 As shown. From Figure 3 It can be seen that during the preparation of SiO2-XG, the sedimentation effect first increases and then decreases with the increase of ammonium persulfate, reaching its optimal value at 7 mmol / L. However, when the amount exceeds 7 mmol / L, the sedimentation effect gradually decreases again. This may be because insufficient ammonium persulfate leads to slow degradation of xanthan gum, and the incomplete degradation mainly involves side chain breakage. The high viscosity of the xanthan gum low-molecular-weight solution makes it difficult for the subsequent SiO2 powder to be completely dispersed. The low concentration of free radicals and the low grafting rate between SiO2 and xanthan gum also affect the sedimentation effect. When the amount of ammonium persulfate is too high, it leads to excessive oxidation of xanthan gum to generate small molecule carboxylic acids or may cause side reactions, resulting in uncontrollable products, performance degradation, or safety risks. At the same time, it will intensify the coupling termination reaction, increasing the probability of termination reactions between xanthan gum free radicals and between xanthan gum free radicals and primary free radicals, thus affecting the grafting rate between SiO2 and xanthan gum and further affecting the sedimentation effect.

[0042] 4. Effect of SiO2 addition during pickling on sedimentation effect In the preparation method of Example 1, the amount of SiO2 used in step (1) was selected to be 0.1~0.5 mol / L, and silica-grafted xanthan gum precipitants with different SiO2 addition amounts were prepared. The sedimentation effects of silica-grafted xanthan gum precipitants with different SiO2 addition amounts are as follows: Figure 4 As shown. From Figure 4 It can be seen that the sedimentation effect during the preparation of SiO2-XG increases with the increase of SiO2 addition, reaching its optimal value at 0.4 mol / L. However, the sedimentation effect gradually decreases when the addition exceeds 0.4 mol / L. This may be because when the amount of SiO2 is insufficient, the surface active sites are insufficient, the grafting reaction is limited, and the grafting rate is low. At this time, there is less SiO2 near xanthan gum, and SiO2 itself is not easy to agglomerate, so the grafting copolymerization reaction is dominant. As the SiO2 content increases, the number of monomers grafted by each free radical increases, so the grafting rate increases and the sedimentation effect improves. When the SiO2 content is too high, SiO2 is prone to agglomeration, the effective specific surface area decreases, hindering the diffusion of xanthan gum molecules and reducing the grafting rate. Furthermore, when the SiO2 content is too high, the monomers aggregate together, which reduces the probability of ammonium persulfate decomposition free radicals attacking the xanthan gum macromolecular chain, increasing the probability of SiO2 agglomeration and affecting the grafting rate, thus affecting the sedimentation effect.

[0043] III. Examination of Usage Conditions The silica-grafted xanthan gum settling agent prepared in Example 1 was subjected to indoor settling experiments to provide a reference for the settling of residual acid and the recovery and utilization of phosphorus resources in the settling residue.

[0044] 1. Testing Method Sedimentation experiments were conducted in a graduated cylinder, and the sedimentation effect was determined by the volume of the supernatant and the volume of the precipitate during the sedimentation process. The residual raffinate used in the experiment was preheated at 70℃ for ten minutes, removed, stirred evenly, and 100 mL of the residual raffinate was accurately measured and poured into the graduated cylinder. Then, 0.5 mL of polyacrylamide flocculant (PAM) was added and dispersed evenly for 60 seconds. Next, the prepared SiO2-XG was added, and after further dispersion, the cylinder was placed in a 70℃ water bath for natural sedimentation at a constant temperature. The height of the clarified layer was recorded at regular intervals. Following the above steps, the optimal preparation method of the sedimentation agent was determined by changing the reaction conditions and the amount of raw materials.

[0045] 2. Effect of SiO2-XG dosage on sedimentation effect The dosages of SiO2-XG were selected as 0.2, 0.4, 0.6, 0.8, and 1 mL. The dosage curves of SiO2-XG are shown below. Figure 5 As shown. From Figure 5It can be seen that as the amount of SiO2-XG increases, the sedimentation effect of the raffinate first increases and then decreases, with the optimal amount being 0.4 mL. Furthermore, it can be observed that when the amount of SiO2-XG is low, raffinate produces sedimentary flocs, but the upper layer is relatively turbid and sedimentation is slow; when the amount of SiO2-XG is high, increasing the viscosity of the raffinate actually hinders sedimentation.

[0046] 3. The effect of dispersion time on sedimentation effect After adding SiO2-XG to the residual acid, the dispersion time was adjusted to study the effect of different dispersion times on the sedimentation effect. The results are as follows: Figure 6 As shown. From Figure 6 It can be seen that when the dispersion time is between 20s and 80s, the optimal dispersion time after adding SiO2-XG is 40s. As the time continues to increase, both the sedimentation rate and the compression ratio (the ratio of the volume of the clear acid to the volume of the sediment) of SiO2-XG decrease. This may be because when the dispersion time is too short, the flocculant cannot mix evenly with the residual acid, resulting in insufficient contact and a decrease in sedimentation effect, and the local aggregation of the flocculant leads to waste; when the time is too long, the flocs formed by sedimentation will be re-dispersed, reducing the sedimentation speed and effect.

[0047] 4. The effect of temperature on sedimentation The temperature was adjusted to study the effect of different temperatures on the sedimentation effect, and the results are as follows: Figure 7 As shown. From Figure 7 It can be seen that the higher the temperature, the better the sedimentation effect of the flocculant. When the temperature reaches 90℃, the synergistic use of the flocculant and polyacrylamide still has a very good sedimentation effect, indicating that the flocculant can be used in systems with higher temperatures.

[0048] Temperature also typically affects the effectiveness of flocculants. Higher temperatures and lower viscosity of raffinate are more conducive to sedimentation. However, flocculants are quite sensitive to temperature; high temperatures can easily lead to their decomposition, thus reducing their effectiveness. The system temperature in the raffinate production process is usually 70-80℃. Experimental results show that SiO2-XG exhibits the characteristic that higher temperatures are more conducive to the sedimentation of raffinate, indicating that SiO2-XG has broad application potential as a raffinate flocculant.

[0049] Comparative Example 1 This comparative example provides a method for preparing a silica-grafted flocculant, which differs from Example 1 in that xanthan gum is replaced with sodium alginate. The resulting product is denoted as SiO2-SA.

[0050] Comparative Example 2 This comparative example provides a method for preparing a silica-grafted flocculant, which differs from Example 1 in that xanthan gum is replaced with carboxymethyl chitosan. The resulting product is denoted as SiO2-CMCS.

[0051] IV. Viscosity Test The viscosity change of residual acid in Example 1 before and after precipitation of SiO2-XG and acrylamide was measured using a modular intelligent advanced rheometer. The test was conducted at 25°C. Shear rate change curves were plotted, and the results are shown below. Figure 8 As shown in (a). From Figure 8 (a) It can be seen that the shear viscosity of the residual acid before and after sedimentation gradually decreases with increasing shear rate, i.e., it exhibits shear thinning, indicating that both are pseudoplastic fluids. At the same shear rate, the apparent viscosity of the residual acid after sedimentation decreases significantly.

[0052] Indoor sedimentation experiments were conducted on the silica-grafted flocculants of Comparative Examples 1 and 2, and the silica-grafted xanthan gum flocculant of Example 1. In these experiments, after 30 minutes of natural sedimentation at a constant temperature, the supernatant was collected for viscosity testing. The viscosity differences between the sediments reflected changes in their solid content and compositional characteristics. The redispersibility time after adding SiO2-XG was 40 seconds, while the redispersibility time after adding the silica-grafted flocculants of Comparative Examples 1 and 2 was 60 seconds. The viscosity test results are as follows: Figure 8 As shown in (b), at the same shear rate, the raffinate treated with SiO2-XG and acrylamide had the lowest shear viscosity, while the raffinate treated with SiO2-carboxymethyl chitosan and acrylamide had the highest shear viscosity. This indicates that the raffinate treated with SiO2-XG and acrylamide can obtain a clearer supernatant with lower viscosity after 30 min of sedimentation with less dispersion time, and has the best sedimentation performance.

[0053] V. Analysis of Settling Sludge 1. Testing Method The sedimentation experiment was conducted in a graduated cylinder, and the sedimentation effect was determined by the volume of the supernatant and the volume of the sediment during the sedimentation process. The residual raffinate used in the experiment was preheated at 70°C for ten minutes, removed, stirred evenly, and 100 mL of residual raffinate was accurately measured and poured into the graduated cylinder. Then, 0.5 mL of polyacrylamide flocculant (PAM) was added and dispersed evenly for 60 s. Then, 0.4 mL of the prepared sedimentation agent was added, and it was dispersed evenly again for 40 s before being placed in a 70°C water bath.

[0054] The products of Example 1, Comparative Example 1, and Comparative Example 2 were subjected to sedimentation, and the resulting products were analyzed.

[0055] 2. Infrared spectroscopy analysis Infrared spectra of sediments obtained from treatment with different flocculants and acrylamide are as follows: Figure 9As shown. 431, 3458, 3441cm -1 The peaks at 2408 and 2404 cm⁻¹ are attributed to the stretching vibration of -OH. -1 The peaks at 1639 and 1635 cm⁻¹ can be attributed to the stretching vibration of the pH bond. -1 The peaks at 1278, 1290, and 1272 cm⁻¹ are attributed to the bending vibration of the OH radical in water. -1 The peaks at approximately 1145, 744, and 630 cm⁻¹ are absorption peaks due to the stretching vibration of P=O. -1 The peaks on the left and right correspond to the asymmetric stretching mode of the Si-O-Si bond and the symmetric stretching vibration of the Si-O-Si bond; simultaneously, the peak at approximately 1067 cm⁻¹... -1 The peaks at 980 and 971 cm⁻¹ are Si-O stretching vibration peaks; -1 The peak at approximately 590 cm⁻¹ is attributed to Si-OH. -1 The peaks around 503 cm⁻¹ represent the stretching vibrations of the Fe-O bond. Additionally, the peak at approximately 503 cm⁻¹... -1 The peaks around the 0.5° mark are stretching vibration peaks of the CI bond. Therefore, the FTIR spectrum indicates that the sediment is a complex mixture.

[0056] 3. XRD Analysis The XRD results of the sediment formed by SiO2-XG and acrylate precipitate residual acid in Example 1 are as follows: Figure 10 As shown in the figure, the main components of SiO2-xanthan gum type sedimentation slag include: Mn2(Al4Si5O) 18 (CO2) 0.2 Na 0.05 (Mg 1.91 Fe 0.09 (Al4Si5O) 18 (H2O) 0.1 C6H 18 Br2CoO3, C 15 H 11 NO2, (Mg) 0.30 Fe 0.70 )2Na 0.05 (Al4Si5O 18 (H2O) 0.66 、(Ca 0.92 Mn 0.08 (Zn) 0.98 Fe 0.02 PO4)2(H2O)2, Mg 0.34 Fe 1.66 Al4Si5O 18 Mg 1.80 Fe 0.136 Al 3.843 Si4.838 O 18 (H2O) 0.86 Mg2Bi 0.116 (Al4Si5O 18 ), NaKCu3O(SO4)3, CaZn2(PO4)2(H2O)2, Sn(H2O)C l2 H2O, HIC l4 (H2O)4, (H3O)(Al3(H2PO4)6(HPO4)2)(H2O)4, (Ca2(H2O)2)(Mn3O2(PO4)3)(H2O), Na2(Zr 0.8 Sn 0.2 Si4O 11 (H2O)2、C6H 18 Br2CoO3.

[0057] 4. XPS Analysis The chemical composition and chemical bond structure of the sediment were analyzed using an X-ray photoelectron spectroscopy analyzer (Thermo Scientific K-Alpha, USA). The spectrum curves were fitted using Avantage software, and the standard C-C binding energy of 284.80 eV was used as the calibration benchmark.

[0058] The chemical composition of the sediment obtained by adding SiO2-XG flocculant and acrylic acid amide during the sedimentation process was analyzed using XPS. The full spectrum of the sediment is shown below. Figure 11 As shown, the main peaks of elements such as O, C, P, Al, Mg, Ba, S, Cr, N, Ca, Sn, and K can be observed, further verifying that the sediment is a complex mixture. Table 2 shows the content of each element. To further confirm the chemical bond situation of each element in the sediment, the 1s and 2p orbitals of these elements were precisely scanned. Figure 12 and Figure 13 As shown: (a) C 1s, (b) Al 2p, (c) Ca 2p, (d) Mg 1s, (e) Fe 2p, (f) F 1s, (g) S 2p, (h) P 2p, (i) N 1s and (j) O 1s. In the sediment, C mainly exists as C-C, CO-C, OC=C, etc.; Fe, Mg, Ca, Al, and F mainly exist as metal oxides; P mainly exists as metal phosphates; S mainly exists as metal sulfates; N mainly exists as amino nitrogen and protonated amino groups (-NH3). + , -NH2 + -) exists in the form of O; O mainly exists in the form of metal hydroxides and carbonates.

[0059] Table 2 XPS analysis results of sediment

[0060] 5. EDS Analysis The microstructure of the sediment was observed using field emission scanning electron microscopy combined with energy dispersive spectroscopy.

[0061] Table 3 and Figure 14 The EDS analysis results of the sediment are shown. Similar to the XPS results, P, C, and O are the three elements with the highest proportions. Because the contents of F, Si, and Cl are too low, their contents are shown as 0 in the EDS results. Figure 13 The elemental distribution diagram shows that F, Si, and Cl elements are present in the sediment.

[0062] Table 3 EDS Analysis Results of Settled Sludge

[0063] The above results indicate that the sediment produced during the raffinate sedimentation process is rich in phosphorus and other metallic impurities, and has certain application potential, such as being used to produce fertilizer and feed-grade phosphates, recover metals, or as an industrial raw material.

[0064] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A silica-grafted xanthan gum settling agent, characterized in that, It is prepared from silica, ammonium persulfate and xanthan gum, wherein the mass ratio of silica, ammonium persulfate and xanthan gum is 1:(0.05-0.09):(0.7-0.9).

2. The silica-grafted xanthan gum settling agent according to claim 1, characterized in that, Silica has a particle size of 25-35 μm and a specific surface area of ​​1100-1300 m². 2 / kg.

3. The silica-grafted xanthan gum settling agent according to claim 1, characterized in that, The silica is acid-washed silica, which is prepared by the following method: silica is mixed with a 1 mol / L hydrochloric acid solution or nitric acid solution and stirred for 20-40 min, then washed and dried to obtain the silica.

4. The silica-grafted xanthan gum settling agent according to claim 3, characterized in that, The mass-to-volume ratio of silicon dioxide to hydrochloric acid or nitric acid solution is 1:0.8 to 1:

1.

5. The silica-grafted xanthan gum settling agent according to any one of claims 1-4, characterized in that, The silicon dioxide is silicon dioxide produced as a byproduct of anhydrous hydrogen fluoride recovery from fluorosilicic acid.

6. The method for preparing the silica-grafted xanthan gum settling agent according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Disperse xanthan gum in deionized water, heat to 45-55℃, add ammonium persulfate to the deionized water, and react for 0.5-2.5 h to obtain a low molecular weight aqueous solution; (2) Add silica to a low molecular weight aqueous solution at 700-900 rpm, then add a 10% ammonium persulfate solution to the low molecular weight aqueous solution under an inert gas atmosphere and at 45-55℃, and stir the reaction at 400-600 rpm for 5.5-7 h to obtain the product.

7. The preparation method according to claim 6, characterized in that, The dosage of ammonium persulfate in low molecular weight aqueous solutions is 5-9 mmol / L.

8. The preparation method according to claim 6, characterized in that, In step (2), the amount of silica used in the low molecular weight aqueous solution is 0.1~0.5 mol / L.

9. The use of the silica-grafted xanthan gum precipitant according to any one of claims 1 to 5 in the preparation of raffinate precipitant.

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